WASHINGTON (AP) -- The top U.S. military officer says it will take two years of study and billions of dollars to overcome the loss of security to military operations and tactics that were revealed in the massive stash of documents taken by former National Security Agency contractor Edward Snowden.

Joint Chiefs Chairman Gen. Martin Dempsey tells the House Armed Services Committee the Pentagon set up a task force to determine how the documents could be used and how to mitigate the problem. He says the task force will take two years due to the "magnitude of this challenge."

U.S. officials have said that the vast majority of the documents taken by Snowden related to U.S. military capabilities. Less than 10 percent involved domestic surveillance programs that have been discussed more widely.